Originally posted by: exdeath
Originally posted by: Zenmervolt
Originally posted by: fbrdphreak
Still, it's a SOHC small displacement V8 so it loses some stump pulling low end torque compared to the larger displacement, OHV designs from GM.
Actually, OHC versus OHV has no fundamental effect on the torque curve. It is simply easier to design an OHC setup to provide better breathing at high RPM than it is to provide good high RPM breathing from an OHV setup, so most companies go that route with OHC, while it's easier to optimize OHV setups for low-RPM power.
You're right about displacement of course.
ZV
EDIT: I am really missing my '06 GT now... Damn Ford.
Really it comes down to port velocites and valve area when it comes to bottom end toque. Intake velocity = stream momentum = continued cylinder filling even at the start of the compression stroke (I know you probably know all this ZV but putting this here for everyone). With a large displacement engine with only 1 intake valve, you are sucking a large volume through a small opening; bingo, instant port velocity and low end torque. With the SOHC 4.6 engine, it all comes down to lack of displacement because both have two valves. It's actually harder to tune the N/A 4v DOHC engines for low end torque due to the lower port velocities that come with a larger valve area. But superior breathing up top, esp. when forced induction is involved, is the tradeoff.
Given the same displacement and valve size there would be zero difference between a OHC or OHV engine except the OHC might rev a little higher and smoother with the lighter valve train having less reciprocating mass.
Also have to look at the resulting effects of displacement, particularly bore size, on the size of the valves. A 6+L 2V engine probably has close to the same valve area as a 4.6L engine with 4 valves. So not only are you down on displacement, already a disadvantage, with 2v OHC your valves are smaller too.
Basically DOHC 4v is essential if you want power out of a small displacement engine like the 4.6. Better yet forced induction is better on 4v engines because you a) solve the problem of bottom end torque by using positive pressure to fill the cylinders instead of relying on port velocities, and b) you fully reap the benefits of the extra breathing of 4 valves when that boost starts piling on heavy at 6,000 RPM. A 2v engine, OHV or OHC, is going to suffer the usually dropping off and running out of breath when winded up high, and it's going to be compounded even more by the blower. Typically once intake velocity exceeds 650 feet per second, you start to LOSE power due to fluid drag, turbulence, etc. It starts costing exponentially more power to suck that air faster and faster (inverse cube law). That is one reason you see the power start falling off after the peak and that fall off occurs lower in the RPMs and is more severe on a 2v engine. The same thing that promotes torque down low is a bottleneck up high. With more valve area, you can flow more air volume without increase the velocity.
I'd pass up this barely more than a GT with a $500 trim package and wait for one of two models that will be significantly set apart from the GT, but not as expensive as the GT500:
The Mach 1 and the GT350.
The Mach 1 is especially unique with lots of changes that are exclusive to the Mach 1 (seats, gauge cluster, hood and shaker scoop, wheels, facia, shift knob, C pillar slope and louvered rear window, DOHC engine similar to the Cobra but not supercharged, all things that are signature Mach 1 traits)
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